An ultrasonic wave is a sound wave which cannot be heard since its frequency is beyond a threshold frequency that a human being can hear as a sound, and since the ultrasonic wave has a short wavelength and high directionality, it can be used in a sonar for measuring depth of a sea, a fish detector or the like by generating a pulse thereof. In addition, in the same principle, the ultrasonic wave can be used to inspect internal defects of a solid material, to cut or process gem/glass or the like, or to create, cleanse and sanitize emulsion.
In addition to this, abnormalities in a human tissue or an animal tissue can be detected using the ultrasonic wave, and there are ultrasonic imaging devices for diagnosing the abnormalities. This makes it possible to confirm the abnormalities in the body of a living creature without dissecting the body. For example, degrees of fatness of organ tissues or thickness of abdominal fat layers can be confirmed by acquiring ultrasonic images of organs of a human body.
Since such an ultrasonography is relatively cheap and convenient to take images and, fundamentally, it does not use radiation, it is safe and non-invasive. Nevertheless, it is disadvantageous in that photographing conditions and photographing techniques are absolutely influential to the quality of ultrasonic images, and reflection characteristics and resolution of the parts through which the ultrasonic waves pass are irregular. Therefore, when various kinds of diagnoses are performed using the photographed images, it is highly probable that a diagnostician arbitrarily interpretes the images, and thus reliability of diagnoses is not perfectly guaranteed.
A phantom used for calibrating an ultrasonic imaging device has been proposed to solve such a problem.
FIG. 1 is a view showing a conventional thickness phantom, and the phantom of FIG. 1 contains a thin plane of a single thickness configured of an echo genic material at a slope of 45 degrees within an anechoic tissue mimicking material.
In order to calibrate an ultrasonic imaging device, the thin plane is scanned using a probe of the ultrasonic imaging device in the direction of 45-degree scan plane from the top surface of the conventional phantom, and a distance to the echo genic line of the acquired image is used as a depth. Since the thin plane is embedded at an angle of 45 degrees, depth to the thin plane from the top surface of the phantom varies depending on the horizontal position of the probe. Accordingly, the ultrasonic imaging device is calibrated by acquiring images while varying the horizontal position of the probe and using a ratio of an actual distance to the thin plane from the top surface of the phantom with respect to the distance to the echo genic line within the image.
If such a conventional phantom is used, an ultrasonic image device which measures a depth several tens of times as thick as a wavelength can be calibrated, and thus a size of an organ in a human body, a size of a fetus in the body of a pregnant woman or the like can be measured approximately.
However, there is a problem in that if the conventional phantom and a method of measuring thickness are used to measure a thickness 0.5 to 3 times as thick as an ultrasonic wavelength, an error occurs in a measured value.
Particularly, thickness of intima, media and intima-media of a blood vessel is used as a diagnostic symptom of a cardiovascular disease and an endocrine system disease, and since thickness of the intima, media and intima-media of a blood vessel cannot be measured using the conventional phantom and the method of measuring thickness, it may create further problems.
Accordingly, required is development of a phantom which can be used to measure thickness of a thin layer 0.5 to 3 times as thick as an ultrasonic wavelength.